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Transcript
The cells environment • 1. All cells live in a fluid environment. – Fluid = moist or water filled. • 2. Cells must obtain nutrients from the outside and release substances into their moist environment. Cell membrane and transport Plasma Membrane • Plasma membrane- the outer boundary of a cell. • Gatekeeper - the plasma membrane prevents certain materials from entering the cell and allows certain materials to pass into the cell. Selectively permeable membrane • Selectively permeable membranemembrane allows certain structures to pass into and out of the cell while keeping others inside or outside of the cell. – Ex. Tea bag. • SPM- maintains the organization of the cell. Lipid Bilayer • Lipid Bilayer- makes up the plasma membrane. – Made up of two layers of phospholipids. • Phospholipid - composed of a phosphate head and a fatty acid tail Phospholipid bilayer • Hydrophilic head - the phosphorous head is attracted to water. • Hydrophobic tails - the fatty acid tails are “afraid” of water. • Results in a two layered (bilayer) membrane Membrane Proteins • Proteins are scattered about the plasma membrane. • Proteins serve as a door in which large molecules can pass through the membrane. • Cholesterol - (lipid) provides rigidity to the cells membrane. Fluid Mosaic Model • Fluid mosaic model - model for the structure of a plasma membrane in which the membrane is a phospholipid bilayer with proteins embedded within it. – Ex. Tile floor • fig 4-8 page 95 Membrane function • Membranes are selectively permeable. • Random movement - “In nature, there is a tendency toward randomness. Energy is required for nonrandomness.” • Diffusion - random movements of ions and other particles. Diffusion • 1. Results in movement of particles from a region of greater concentration to a region of lesser concentration. • Dynamic equilibrium - condition in which there is a continuous movement of molecules but no overall change. Osmosis • Osmosis - the diffusion of water into and out of cells across a selectively permeable membrane. • Osmotic balance - occurs when the movement of water into and out of the cell is equal. – Blood cells – plant cells Types of Solutions • Isotonic Solution – equal concentration of solution and the cell. (Osmotic balance) • Hypotonic Solution – Greater water concentration outside the cell than inside the cell (The cell bursts) • Hypertonic Solution – Greater water concentration inside the cell than outside the cell (The cell shrinks) Passive transport • Passive transport - the cell plays no active role and does no work in moving the particles. Requires no Energy • 1. Water • 2. Lipids • 3. Substance soluble in lipids • 4. very small particles Types of passive transport • 1. Osmosis • 2. Diffusion • 3. Facilitated Diffusion Facilitated Diffusion • Many particles needed by cells must have some help getting across the cell membrane. • Facilitated diffusion - the use of transport proteins to aid the passage of materials across the plasma membrane Transport proteins • 1. Channel proteins - simplest type. These are simply called pores. These serve as channels that allow ions to pass through. – Depend on size and charge. • Even if an ion is small enough to pass through the pore, it may be prevented by its charge. Transport proteins (continued) • Carrier proteins or GATE Proteins- more complex, works like a gate. • 1. A particle on one side of a membrane attaches to a protein • 2. The protein changes shape • 3. Allows the desired particle to pass into or out of the cell. • 4. When the signal molecule is released, the gate closes Active Transport • Active transport - the moving of particles from a region of lesser concentration to a region of greater concentration. – Requires Energy • Pumps - transport proteins used to move a particle through a plasma membrane. – Requires chemical energy to alter the shape of the protein. Active Transport (continued) • Examples of Active Transport • 1. Marine Fish - actively pump out salt even though the concentration of salt is more outside their body. Other methods of entering and exiting the cell. • 1. Endocytosis - the process by which the mambrane engulfs and takes in a substance. – Phagocytosis - solid particles are ingested – Pinocytosis - liquid particles are ingested. • 2. Exocytosis - cell products or wastes are released to the surroundings • see figs 4-17, 18, 19